Project II seeks to carry out a comprehensive study of the structural and chemical variations in dentin from a materials science perspective. Although considerable information is available concerning the basic components in dentin and their development and mineralization, little information is available which links structure and properties of dentin, which is necessary for a detailed understanding of this material. A variety of special techniques and refined high technology instruments has been developed that could facilitate the goal of this project which is to measure the extent and variations in structure and chemistry which occur in dentin as a function of tooth type and location within the dentin. To accomplish this goal we will carry out specific aims that (1) seek to characterize the microstructural features and interactions between the main components of dentin; and (2) define differences in dentin which are dependent on intra tooth location, tooth type and patient history. The characterization process will be conducted using state-of-the-art analytical techniques which include: wet and high resolution scanning electron microscopy (SEM) with energy dispersive x- ray spectroscopy (EDS), wave length dispersive x-ray spectroscopy (WDS) and microprobe, x-ray diffraction, Auger electron spectroscopy (AES), x-ray photoelectron spectroscopy (XOS/ESCA), secondary ion mass spectroscopy (SIMS), Fourier transform infrared (FTIR) spectroscopy, high resolution and analytical transmission electron microscopy (HREM,ATEM), critical surface tension, and permeability. Surface characteristics of freshly cryofractured dentin will serve as a baseline for dentin. Treatments will be established to provide a flat uniform surface with characteristics equivalent to cryofractured dentin to standardize surface preparation for all subsequent studies. The characteristics of dentin as a function of position, tooth type, orientation will be established with consideration given to patient history. This will permit us to assemble a comprehensive model of the structure and chemistry of dentin, be able to detect significant differences and estimate the magnitude of variation as a function of position within teeth and between tooth types. We also hope to make variance estimates on the influence of normal tooth developmental and environmental history. The data from this project will be valuable for understanding dentin structure and property changes from restorative procedures and modification, pathological processes and normal function.